In global positioning system (GPS) based surveying or Geographic Information System (GIS) data collection applications, it is common to employ a number of GPS receivers which share satellite observables. The means for sharing this data is usually via a terrestrial radio link. The GPS receiver processesor and terrestrial radio link form a GPS system.
A typical GPS system network includes a GPS system located on a piece of machinery or a vehicle which receives telemetry data from satellites which is processed via an electronics package located within the GPS system. The GPS system transmits data to other GPS systems and to a fixed observer site. The GPS system also receives and processes data from other GPS systems and from the fixed observer site. Data is transmitted to and received from other GPS systems and the fixed observer site via a Radio network antenna. An antenna is required so as to assure effective data transfer irrespective of the movement or rotation of a given GPS system. The radiation pattern is particularly important since GPS systems are typically used in outdoor environments such as in surveying, moving vehicles, etc. where the orientation of one GPS unit relative to other GPS units and systems is difficult to obtain.
Prior art antennas for Radio networks require the connection of numerous small components. Typically, eight to ten patch antennas are individually fabricated and each antenna is attached to a radio network housing. The attachment of patch antenna to the radio network housing is typically done manually. Each patch antenna must be carefully aligned and exactly placed so as to assure a uniform antenna radiation pattern. Each patch antenna must then be attached to a power source. This is typically accomplished by coupling each patch antenna to a designated point on a parallel feed network circuit. The parallel feed network circuit is coupled to the electronics package which is coupled to the power source. Electrical coupling of each patch antenna to the parallel feed network is typically accomplished by soldering one end of a wire to each patch antenna and soldering the other end of the wire to a point on the parallel feed network circuit.
Patch antenna systems are difficult to design. In particular, in order to design a patch antenna system that will fit into a given container, individual patch antennas radiating at the desired frequency are placed circularly within a housing of the GPS system. In the past, this system has worked relatively well since patch antennas have been used in systems which radiate at a set frequency which is in the range of 2.44 GigaHertz. Due to the high frequency range of the radiation, design of patch antennas conforming to relatively small sizes of containers has been possible.
Recently, there has been a need to place patch antennas around electronics packages within a housing in order to minimize the size of GPS systems and components. This also results in products which are easier to handle and easier to use and which are more durable. Typically, recent prior art GPS systems have been made which have diameters of less than 24 inches. In many cases, depending on the product, such systems are much smaller than 24 inches in diameter.
The process of fabricating patch antenna systems and individual patch antennas is costly and time consuming. Not only is the process of connecting each individual patch antenna to the GPS system housing and to the parallel feed network costly and time consuming; but also, the process of designing a patch antenna array is costly and time consuming. The process of designing patch antenna arrays for different products is particularly time consuming since each size of housing requires a different number of patch antennas. In addition, when an antenna is placed around an electronics package, the pattern of the antenna is negatively affected. In most cases, the uniform characteristics of the resulting pattern is destroyed. In order to compensate for the electronics package, the antenna is typically placed one quarter wavelength away from the electronics package. Though this compensates for the deleterious effects of the electronics package on the antenna's pattern, it increases the size of the resulting product.
Though it would be possible to make patch antenna arrays which operate at the lower frequency ranges, such systems are impractical due to the large size requirements of such systems. Thus, patch antennas which operate in lower frequencies such as, for example, the 450 megahertz range are typically not feasible when the antenna must be integrated into the housing. However, such systems may be manufactured by using a separate antenna which connects to the GPS system or by using an antenna which projects from the top of the GPS system (e.g. a conventional dipole antenna). However, such dipole antennas are not desirable since they do not provide sufficient bandwidth or gain and since they may be easily damaged or broken and it degrades the performance of the GPS antenna that receives satellite signals.
What is needed is a simple antenna which will radiate uniformly and which can be designed to fit into nearly any given size of container. The antenna needs to be durable and reliable and inexpensive to manufacture and assemble. More specifically, an antenna system which will radiate a uniform pattern azimuthally and which will reliably operate in difficult environments such as those presented by mounting the antenna on heavy machinery and vehicles is required. Also, an antenna having a broad bandwidth which is easy and inexpensive to make is required.